1. Field of the Invention
This invention relates to valves and more particularly to gate valves.
2. Description Of The Prior Art
A non-rising stem gate valve with separable seats and automatic plastic sealed gate-seat and seat body interfaces is disclosed in U.S. Pat. No. 2,433,638--Volpin. A similarly sealed valve of the rising stem, balance type intended for high pressure use is disclosed in U.S. Pat. Nos. 3,538,938--Volpin, and 3,696,831--Fowler et al. In the latter two patents chevron stem packing compressed by annular screw plugs is employed for the stem seals.
A valve known as a "Graygate" appears to employ plural but separated metal-plastic-metal sandwich seals around the valve stem and in a bonnet pocket but the metal rings are not of the dished type and are not coined at their peripheries when in use. The seat hub seals are combinations of plastic and metal pieces but also do not show dished type metal rings and are not raised at their peripheries when in use.
It is believed that the valve of the present invention can be used without leakage in environment of higher pressure and over a wider temperature range than the valves discussed above.
Stacked dished packing rings for a pipe hanger are disclosed in U.S. Pat. No. 2,417,181--Sandilands, but Sandilands does not disclose metal rings that are flattened by a compression means, in a seat hub.
Difficulties experienced with dished metal-to-metal seal rings of the type disclosed in U.S. Pat. No. 2,922,840 to Reynolds et al are discussed in my aforementioned U.S. Pat. No. 4,056,272.